Q: You write, "When it
comes to explaining distributions broken up by oceans, biogeography has been as
fickle as fashion. Back and forth the pendulum has swung..." and you ask,
"Why should we believe that we're finally getting it right?" Why do
you think you're finally getting it right?

A: Scientific views change
for a lot of reasons, and, as the philosopher Thomas Kuhn pointed out, only
some of them have to do with actual evidence. I think that, in this case, views
could keep changing because there wasn’t enough evidence or, at least, there
wasn’t enough evidence that enough people agreed was legitimate.

In the absence of evidence,
scientists’ beliefs often were based on intuition—for instance, the feeling
that there’s no way monkeys could have crossed the Atlantic—and on the
influence of certain very persuasive individuals (the ichthyologist Gary Nelson
is one I wrote a lot about in the book).

The difference this time
around is that the swing back to ocean-crossing explanations has been driven by
evidence, especially DNA sequence data that have been used to estimate when
different evolutionary lineages (such as New World monkeys and Old World
monkeys) separated from each other.

The information from DNA
about when things happened is critical for distinguishing between ancient
fragmentation and more recent dispersal, and we suddenly have much, much more
of that information than we had before.

I’ve seen the explosion of
DNA evidence, of course, but there’s also a kind of psychological argument for
my interpretation that this latest swing of the pendulum isn’t a case of people
just believing what they want to believe or have been taught to believe.

The argument is that a lot of
the people who are now saying that ocean crossings are really important
actually started out with a bias against that explanation.

That is, when they began
studying biogeography, they were thinking that continental drift and other
processes that fragment landmasses were the dominant explanations for
distributions broken up by oceans. They had to have their arms twisted by the
evidence to come around to thinking that ocean crossings have been really
significant as well.

Two of the scientists I wrote
about in the book—Miguel Vences, who studies frogs, and Matt Lavin, an expert
on bean plants—followed that kind of an intellectual arc. For that matter, so
did I.

It will be fascinating to see
what happens to this field of study going forward. There are still quite a few
scientists who don’t believe the DNA evidence and haven’t budged from their
view that relying on chance ocean crossings is delusional.

At this point, given all the
evidence that’s piled up, these people seem to me almost like creation
scientists and, like the creationists, I don’t expect them to ever change their
minds. But I suspect that their influence won’t persist much into the next
generation or two of scientists.

Q:Why did you decide on "The Monkey's
Voyage" for the title, and what is especially intriguing about the
monkey's journey?

A: I chose that title for two
reasons, one obvious and one almost completely cryptic. The obvious one is that
the case of monkeys rafting across the Atlantic is probably the most startling,
well-established illustration of a natural colonization across an ocean.

The book kind of builds up to
that as the centerpiece example (although the fundamental conclusions wouldn’t
be changed even if that example didn’t exist). It’s a case that’s especially
surprising because it involves land mammals, animals that aren’t supposed to be
able to survive long ocean journeys.

What I hope readers take from
that example is something like “Wow, if monkeys crossed an ocean, lots of other
species must have done it also.”

The less obvious reason for
the title—and sort of an inside joke—comes from the notion that humans are
monkeys; that is, we’re one, admittedly peculiar, species within the monkey
evolutionary group.

That idea was in my mind when
I was writing the book, so the phrase “the monkey’s voyage” almost invariably
made me think about my own intellectual journey and those of other scientists
who have explored this subject. On the cover of the book, my name is right
under the image of the monkey, which I think is perfect, because I’m the
monkey.

Q: You write that without
chance ocean crossings, life would be very different today. What are some of
the most notable examples?

A: There are several levels
of answers to that question. A somewhat superficial, but still striking answer
is that many species that people use frequently wouldn’t even exist if their
ancestors had not crossed oceans naturally.

Some of the many examples
include the common bean, squash, the most widely-used cotton species,
watermelon, eggplant, nutmeg, and guinea pig. If you took away those species,
the history of humans would certainly be different, probably radically
different.

For instance, without beans
and squash, the indigenous cultures of North America could not have developed
as they did, and those differences would have affected the course of European
colonization, and on and on down the line.

A deeper answer is that there
have been so many successful colonizations across ocean barriers that, if you
could make all of them disappear from the history of life, the entire biota of
the world would be almost unrecognizable. It would be like an alien planet.

For instance, well over half
of all living land mammal species in South America—the monkeys and almost all
of the rodents, things like the capybara and guinea pig—are the descendants of
mammals that crossed a sea or ocean to get there.

But it isn’t enough to just
imagine subtracting those species from the modern biota; the immigrant rodents
and monkeys undoubtedly have had huge effects on the evolution of other groups,
including other vertebrates, various kinds of parasites, and plants. And the
mammals are just one of many South American groups that include overwater
colonists, so the total influence of these colonizations is hard to even
fathom.

In the book I focused on
South America to make the point about the great influence of ocean crossings,
but I think you could make a similar case for almost any part of the world.
From this, it follows that the global impacts must be enormous.

Finally, there are fossils
that suggest that the anthropoid primates originated in Asia, and that members
of this group dispersed to Africa something like 50 million years ago.

If that’s true, it means that
these ancient primates had to raft across the sea, because Africa was an island
at the time. Now, these African anthropoids were the ancestors of all living
monkeys and apes, which means that they were our ancestors.

So, if you took away just
that one chance sea crossing, humans would never have evolved, which is an
interesting thing to ponder. There would be a lot less carbon dioxide and other
greenhouse gases in the atmosphere, the planet would be cooler, there would be
many more species of native island birds, more forest, more fishes and whales
in the ocean, and nobody would have written anything about biodiversity or
anything else for that matter.

Q: What are you working on
now?

A: I just took a short trip
to the California coast to collect some jumping bristletails that will,
hopefully, help us figure out whether these flightless insects colonized Hawaii
from North America or the other way around, something I mentioned in the book.

We may also have discovered a
new species of bristletail, which I’m irrationally happy about. There’s a
saying about scientific contributions—“theories pass, the frog remains.” And
this new bristletail hopefully will remain too.

On the writing side, I’m
thinking about another general audience book on evolution, but the ideas are a
little bit fluid at this point. However, I’m pretty sure that this next book
will deal with humans and the human condition, but without being about the
usual sorts of things categorized as “human evolution.”

That is, it won’t be about
how we got opposable thumbs, or became bipedal, or ended up as the only
surviving human lineage. I hope it will be the kind of book that will make
people think about a lot of things they’ve never considered before.

Q: Anything else we should
know?

A: Just something to get rid
of a little guilt: In reading reviews of my book, I’ve noticed that people
often talk about my “far-flung travels” in a positive way. And I know that, in
at least one place in the book, I implied that journeys to exotic places to
encounter exotic creatures are really desirable.

However, given the fact that
traveling great distances in fossil-fuel-powered planes and cars generally
isn’t in the best interests of the ocean-crossing and other organisms on this
planet, it’s hard to sustain an entirely positive view of world travel.

I won’t say that traveling is
bad, period, or that I’ll never again take a big international trip, but I do
think that, in this era of obscene consumption that’s driving environmental
destruction, we shouldn’t be glorifying exotic travel as I did in the book.

Maybe, instead, we should
emphasize the exploration of our own backyards a little more. From a
biologist’s perspective, for instance, there are intriguing species to be seen
and discoveries to be made anywhere.

I’ve done a fair amount of
traveling—certainly too much—both within and outside the U.S., but the first
new species I ever had a part in discovering was a bristletail insect that
lives in mountains we could see from our dining room windows.

Also, the most satisfying
contemplative experiences I’ve had within the natural world usually have been
in familiar places, where I’m comfortable and have some history, so that’s
another argument (at least for me personally) for staying put.

About Me

Author, THE PRESIDENT AND ME: GEORGE WASHINGTON AND THE MAGIC HAT, new children's book (Schiffer, 2016). Co-author, with Marvin Kalb, of HAUNTING LEGACY: VIETNAM AND THE AMERICAN PRESIDENCY FROM FORD TO OBAMA (Brookings Institution Press, 2011).